[person] (January 28, 1909 - February 11, 1972) A Canadian-American geneticist. He received his MD from McGill University in 1932, at the age of 23. Working with Oswald Avery and Maclyn McCarty, MacLeod showed that changes in the form or function of bacteria are caused by changes in DNA. The Avery-McCarty-MacLeod experiment was vital in the discovery that genetic material is contained in DNA, not in protein. Later in life, MacLeod became involved in health issues related to the Second World War, such as the microbial diseases typhus fever, malaria, and pneumonia, which posed serious threats to military personnel.

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[noun] Nutrients that are needed in high amounts to sustain life. For example, plants need a high amount of nitrogen, phosphorus, and potassium in order to grow and reproduce. See also: limiting nutrient and micronutrient.

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[adjective] That which is observable by the unaided eye. Many scientific disciplines explore both large-scale (macroscopic) and tiny (microscopic) properties to fully understand phenomena and organisms. Contrast with microscopic.

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[person] (Portuguese: Fernão de Magalhães, ca. 1480 - April 27, 1521) A Portuguese explorer who became a Spanish national so that he could search for a westward route to the Spice Islands (modern Indonesia) for King Charles of Spain. Magellan's expedition of 1519 - 1522 was the first to sail from the Atlantic Ocean to the Pacific Ocean, and the first to cross the Pacific. The expedition completed a circumnavigation of the globe, but Magellan was killed in battle in the Philippines. Magellan named the Pacific Ocean (from Latin, meaning the peaceful ocean), which he reached via what he named the Straits of Magellan. He also named the Magellanic penguin; he was the first European to describe it. He is remembered as one of the great explorers, and the Magellanic clouds, nearby dwarf galaxies visible from the southern hemisphere are named after him.

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[noun] A measure of an object's interaction with an external magnetic field. A magnet, an electron, and a planet all have magnetic moments. For particles, the magnetic moment is caused by the spin and charge of the object.

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[noun] Magnitude is a number assigned to a quantity and refers to the size or extent of something. There are several differing scientific uses of the term. In physics, it refers to the quantity of a measurement such as length, in astronomy it may refer to the brightness of a star, while in geology, it can indicate the strength of an earthquake.

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[person] English ordained minister and economist born in Dorking, Surrey (1766-1834). In 1798 he published his Essay on Population, suggesting that a given population will always exceed its food supply, and it would therefore be counterproductive to provide starving populations with food. Instead, he argued, social equality must be achieved through other means, such as universal suffrage and state-funded education for the poor.

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[noun] The middle portion of the interior of the Earth, starting below the crust at 5-70 km below the Earth’s surface and continuing to a depth of 2900 km. The mantle is composed mainly of the rock peridotite.

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[noun] A fundamental property of matter which is a numerical measure of the inertia of an object or the amount of matter that an object contains. The mass of an object is different from its weight as mass is independent of the gravitational field exerted on an object.

[noun] A spectrometer that measures the composition of samples by analyzing the mass to charge ratio (m/z) of components in the sample. To do this, the sample introduced into the spectrometer is ionized under high energy, and the various ions are then separated in a magnetic field and measured. The specific m/z signature of each ion is then used to identify the parent element or compound.

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[verb] The process of analyzing and describing real-life situations using appropriate mathematics and statistics. Modeling is often used to express a situation as an equation and to use the equation to better understand the situation and make better future decisions about it.

[person] English marine geophysicist, born in Porlock, Somerset (1931-1997). In 1962, Matthews participated in the International Indian Ocean Expedition and made a detailed survey of a submarine ridge that showed that the pattern of magnetic polarity of seafloor rocks surrounding the ridge was symmetric. This discovery contributed to the widespread acceptance of the plate tectonic theory. He also studied the structure and evolution of continental crust using deep crustal seismics.

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[person] (1806-1873) American naval officer and chronicler of winds, currents, and other observations. Maury led the effort to standardize meteorological observations so that they could be shared and compiled more easily. He is best known for his publication, The Physical Geography of the Sea and its Meteorology, first published in 1855.

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[noun] In aquatic sciences, the deepest part of a specified area, such as a lake or gulf. Depth is an important factor in aquatic systems because it influences the water body’s overall temperature, water volume, and its ability to sustain plant and animal life. Shallow ponds, for example, will be warmer overall than deeper ponds in the same geographical region because they have a greater surface area/depth ratio, and so the available sunlight warms the water to a greater extent.

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[person] Scottish theoretical physicist and mathematician born in Edinburgh (1831-1879). Maxwell developed the classical electromagnetic theory, which synthesized previously unrelated observations, experiments, and equations of electricity and magnetism. In 1864, Maxwell wrote A Dynamical Theory of the Electromagnetic Field, in which he proposed that light is a wave. He also described what is now known as Maxwellian distribution, a statistical way of describing the kinetic theory of gases.

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[person] (June 9, 1911 - January 2, 2005) An American physician and geneticist who specialized in infectious diseases. McCarty is remembered for discovering, with Oswald Avery and Colin MacLeod, that DNA is responsible for changes in form and function of bacteria. McCarty's later work focused on rheumatic fever and its relationship to the Streptococcus bacteria, and he pioneered the now-standard medical practice of using protein levels in blood to measure rheumatic inflammation.

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[noun] In statistics, mean commonly refers to the arithmetic mean, also called the average, which is one measure of the mid-point of a dataset. The mean and median approach one another in datasets that approach a normal distribution, but can differ substantially in datasets with skewed distributions. Compare to median. The mean is calculated by obtaining the sum of the values in a dataset and dividing that sum by the number of data points, as in the formulas shown.

[person] English biologist and essayist born in Brazil (1915-1987). Though he initially studied zoology, he became more interested in medicine in graduate school. With Sir Frank MacFarlane Burnet, Medawar won the Nobel Prize for Physiology or Medicine in 1960 "for discovery of acquired immunological tolerance"; Medawar's work concerned skin grafting and other organ transplants in humans. In his later years, he became a prolific author about the nature of science, and is well known for his essays "The Art of the Soluble" and "The Phenomenon of Man."

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[noun] In statistics, the median is the value separating the upper half from the lower half of a dataset. In other words, it is the middle value of the data when they are arranged in order of magnitude. The median is a characteristic of a dataset comparable to the mean. The median and mean approach one another in datasets that approach the normal distribution, but can differ substantially in datasets with skewed distributions. Compare to mean.

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[noun] Process, occurring in sexually reproducing eukaryotes, in which a single cell divides twice, yielding four cells, also called gametes, each of which is haploid (it contains half the genome of the organism). In males, gametes produced are called sperm, whereas gametes produced by females are called ova, or eggs.

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[noun] The temperature at which a compound is transformed from its solid state to its liquid state, and where the solid and liquid states exist in equilibrium. During the transition from solid to liquid, the energy put into the system goes to changing the compound’s state, not increasing the temperature, so the temperature remains constant until the solid is completely melted.

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[person] Austrian Augustinian monk and scientist born in Heizendorf (now Hynice, Chech Republic) (1822-1884). In 1865, Mendel wrote Versuche über Pflanzen-Hybride (Treatises on Plant Hybrids), which detailed his observations on the inheritance of various traits in cross-bred pea plants and presented his principles of hereditary transmission. Unfortunately, the importance of his work was not recognized until after his death.

[person] Russian inventor and chemist born in Tobolsk, Siberia (1834-1907). Mendeleev's most famous work is the development of the periodic table of elements, and his prediction of properties of elements that were, at that time, not yet discovered. In 1869, Mendeleev helped found the Russian Chemical Society. He researched in many fields, including physics, hydrodynamics, meteorology, and chemical technology.

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[noun] A sequence of biochemical reactions in living organisms that converts food into energy used to drive other biological processes. Also, the sequence of transformations foreign compounds undergo inside a living cell.

[noun] A bond between two metal atoms. Metallic bonds are strong and non-directional, meaning that it is hard to separate metal atoms but they can move and remain bonded as long as some parts of their surfaces are in contact. The outer electrons are relatively free to move between bonded metal atoms.

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[adjective] Formed through the processes involved in metamorphism, which include deep burial, exposure to high temperatures and pressures, and interactions with hydrothermal fluids. Metamorphic rocks are generally considered to have a parent rock, or protolith, which can be any rock type. The minerals and textures that are produced through metamorphism are indicative of both the protolith and the metamorphic environment.

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[noun] Physical and chemical changes to rocks that occur below the Earth's surface. These changes are caused by increased temperature, increased pressure, and the presence of hydrothermal fluids, and result in the growth and reorientation of crystals in the rock. Metamorphism does not include melting - once magma forms, the resulting rock will be igneous.

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[person] English natural philosopher and geologist, born in Nottinghamshire (1724-1793). In 1750 he published A Treatise of Artificial Magnets, detailing his observations on the variations in forces between magnetic poles. He also demonstrated radiation pressure, adding support to Christian Huygens' argument that light consists of waves.

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[person] American physicist, born in Strelno, Prussia (1852-1931). He is remembered for his work in optics, particularly for his early, extremely accurate experiments to determine the velocity of light. Michelson invented the interferometer, which he used to determine the effect of Earth's motion on the observed velocity of light. He was also interested in astronomy, and, using his interferometer, accurately measured the diameter of the star Betelgeuse. He was awarded a Nobel Prize in physics in 1907.

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[noun] Nutrients that are needed to grow and reproduce, but in small amounts. For example, plants need boron in order to develop fruits and seeds. However, the amount of boron needed to perform this function is much less than the amount of nitrogen the plant needs to perform photosynthesis. In humans, supplements generally labeled as vitamins fall into the micronutrient category. See also: limiting nutrient and macronutrient.

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[adjective] That which cannot be seen with the unaided eye and requires a tool (such as a microscope) to view. Many scientific disciplines explore both large-scale (macroscopic) and tiny (microscopic) properties to fully understand phenomena and organisms. Contrast with macroscopic .

[noun] Microtubules are hollow cylinders of tubulin protein in the cytoplasm of all eukaryotic cells. As part of a cell's cytoskeleton, they shape and support it. Microtubules are also involved in the transport of materials inside of the cell. They serve as paths along which organelles with motor-equipped molecules can move. Microtubules participate in the separation of chromosomes during cell division (mitosis) and can act alone or form such complex structures as flagella and cilia.

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[noun] A linear, elevated region of the ocean floor where magma is upwelling and extruding, and new crust is forming. The ridges are often referred to by their more specific names: Mid-Atlantic Ridge, East Pacific Rise, etc.

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[noun] European history from the 5th century to the 15th century. The Middle Ages follow the fall of the Western Roman Empire in 476 and are marked by depopulation, migration from urban centers, and increasing frequency of barbarian invasions. Key events include the Crusades, during which Europeans attempted to recapture the Holy Land, and the development of the serf system, which enabled systematic agriculture to begin again. Agriculture was widely affected due to climate change, resulting in frequent famines. In addition, the Black Death (which may have been the bubonic plague) spread rapidly across Europe, killing 30-60% of the population by the mid-14th century. With the resulting decrease in the labor force, due to death by disease or hunger, landlords were forced to offer higher wages to entice peasants to work in their fields. The end of the Middle Ages is generally considered to be 1453, the date of the Turks' conquest of Constantinople.

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[person] A Swiss physician and biologist (1844 - 1895). An attack of typhoid fever left him partially deaf, and he felt this would be a disadvantage as a doctor, so he decided to pursue physiological chemistry instead. He is remembered for isolating nucleic acids from white blood cells, one of many steps that made possible the discovery that DNA carries genetic material. In addition, Meischer proved that breathing is regulated by carbon dioxide concentrations in the blood.

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[noun] A naturally formed, inorganic solid with a specific chemical composition and characteristic crystal structure. Examples of minerals include quartz (SiO2), salt (also called halite, NaCl), and graphite (C). Rocks are formed of one or more minerals.

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[noun] Process occurring as part of the eukaryotic cell cycle. In mitosis, chromosomes in the cell nucleus separate into two identical chromosome sets, the two sets are separated, and two independent nuclei form, each with its own set of chromosomes matching that of the parent nucleus. Mitosis consists of five stages: prophase, prometaphase, metaphase, anaphase, and telophase.

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[person] Croatian meteorologist and geophysicst born in Volosko (1857-1921). In 1901, Mohorovičić was appointed head on the meteorological service of Croatia and Slavonia. He upgraded the services to European standards, and expanded the work of the observatory into seismology, geomagnetism, and gravitation. Mohorovičić discovered the existence of S and P seismic waves, which propagate through the Earth at different velocities. From seismic refractions, Mohorovičić discovered a discontinuity between the less dense rocks of the crust and denser rocks of the mantle, now called the Mohorovičić discontinuity (known more commonly as the Moho).

[noun] The boundary within the Earth between the crust and the mantle, as indicated by the refraction and velocity change of seismic waves recognized by Andrija Mohorovičić. The depth of the Mohorovicic Discontinuity is ~5-7 km below oceanic crust and ~10-70 km below continental crust.

[person] German geologist and mineralogist born in Gernrode (1773-1839). In 1802, after studying at the Mining Academy in Freiberg, Saxony, Mohs moved Austria, where he was hired to identify minerals in a private collection. In order to do this, he classified the minerals by their physical characteristics rather than their chemical compositions (as was usually done). He developed the Mohs' hardness ^~scale, a relative ^~scale of the hardness of minerals that remains a useful way to identify minerals in the field.

[person] (September 25, 1866 - December 4, 1945) An American embryologist who won the Nobel Prize in Physiology or Medicine in 1933 for his discoveries about the role that chromosomes play in heredity. Morgan's most important book, The Mechanism of Mendelian Heredity, with several coauthors, was published in 1915 and became a fundamental work in the field of genetics. Morgan's later work focused on embryology and on encouraging the use of genetics research and a mechanistic approach in all fields of biology.

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[noun] A story, idea, or concept invented with a purpose. Myths are generally intended to explain the relationship between gods or natural forces and humans. The events in myths are often impossible, but myths contain important social or religious information for the population that has created them.